All work in my section began in February 2017, so there are no CCR-based accomplishments to report yet. Nonetheless, we have generated a large panel of novel IFITM3 mutants to aid in our study. Furthermore, we have developed systems using MLV-based vectors and adapted a pseudotyping procedure to study how various retroviral glycoproteins affect viral susceptibility to IFITM-mediated antiviral activities. Our data thus far suggest that IFITM3 exhibits great breadth with regard to its ability to inhibit retroviral particle infectivity. These findings suggest that these antiviral proteins may impose serious barriers to multiple mammalian retroviruses of medical importance in different species.